(a) Field of the Invention
The present invention relates to an electronic musical instrument, and more particularly it pertains to a digital electronic musical instrument of a waveshape memory type.
(B) Description of the Prior Art
In an electronic musical instrument of a waveshape memory type, the waveshape of the musical tone signal is preliminarily stored in a memory means and is read out upon each key depression at a predetermined speed corresponding to the tone pitch of the depressed key. An example of such an electronic musical instrument of a waveshape memory type is shown in FIG. 1. When a key in a keyboard 10 is depressed, a key-on signal KON is generated from the keyboard means 10. Also, the key depression actuates a reference number memory 11 (referred to as R number memory hereinbelow) to generate a reference number (referred to as R number hereinbelow) which is related with the depressed key and is proportional to the fundamental frequency of a tone to be sounded. The R number read out from the R number memory 11 is transferred to a cumulative adder 13 through a gate 12 which is controlled by a clock pulse .phi. of a constant period. The adder 13 cumulatively adds the R number supplied from the R number memory 11 at the timing of said clock pulse .phi. and supplies the temporary sum to a waveshape memory 14 as its address signal. Namely, the adder 13 delivers R (number below radix point, in general) at the timing of the first pulse .phi., 2R at the timing of the second pulse .phi. and similarly qR at the timing of the q-th pulse .phi., to call the addresses of the respective waveshape samples in the waveshape memory 14. The adder 13 contains integer digits and fraction (below radix point) digits and has a modulus of a certain number, e.g. 128. Thus, the output of the adder 13, x = qR (q = 1, 2, . . . ), increases from zero to the modulus with a pitch of R, and when the sum exceeds the modulus, the difference between the sum and the modulus is left in the adder 13 and similar cumulative addition is performed thereon. Since the R number added to the adder 13 is proportional to the fundamental frequency of the musical tone to be sounded, the rate of change of the sum x = qR, i.e. the repetition frequency of the stepping-up in the adder, is also proportional to the fundamental frequency of the musical tone to be sounded. Therefore, when the number of stages or memory samples in the waveshape memory 14 is set equal to the modulus of the adder 13, the frequency of the waveshape production from the waveshape memory 14 also changes in proportion to the magnitude of the R number. In other words, when the number of samples in the waveshape memory is 128 and the timing pulse .phi. has a repetition period of T.sub.0, the repetition frequency f of the waveshape production from the waveshape memory 14 becomes f = (R/T.sub.0)/128 = R/(128.multidot.T.sub.0) (Hz). That is, when a larger R number is generated, the output of the waveshape memory 14 varies rapidly and the repetition period of the waveshape production becomes short to generate a high frequency musical tone. On the other hand, when a small R number is generated, a low frequency musical tone is produced. The details of such functions are disclosed in Japanese Patent Laid-open Publication No. 48-90217 (corresponding to U.S. Pat. No. 3,809,786 to Ralph Deutsch issued on May 7, 1974).
The digital information read out from the waveshape memory 14 and constituting the waveshape of the musical tone of a desired tone pitch is multiplied with an envelope information derived from an envelope generator 15 in a multiplier 16 to be afforded with a tone envelope and then it is transferred to a digital-to-analog (D/A) converter 17 to generate a corresponding analog signal. This analog signal is sounded as a musical tone in a loudspeaker 19 through an audio device 18 including an amplifier, etc.
The envelope generator 15 is activated by the key-on signal KON as shown in FIG. 2A generated by the depression of a key in the keyboard 10, and gives an envelope ENV as shown in FIG. 2B having the attack, the first decay to sustain and second decay, envelopes ENV.sub.1, ENV.sub.2, and ENV.sub.3 to the waveshape signal generated from the waveshape memory 14 to form an expressive musical tone signal. That is, the envelope of FIG. 2B shows how the musical sound grows to the maximum amplitude upon depression of a key (attack), attenuates to a sustain level (first decay), keeps the constant amplitude (sustain), and gradually vanishes (second decay) upon release of the key.
As can be seen from the statement made above, according to the above-mentioned electronic musical instrument of a waveshape memory type, since the information of a predetermined waveshape is stored in the memory, the musical sound to be generated has only a variable envelope with a fixed tone color from the attack to the last decay. This is far from the rich sound of a natural musical instrument. A natural musical sound has a variable tone color from the attack to the decay.